Just five years ago, Joan Smalls was a struggling model—living at her aunt's apartment in Queens, New York, taking the bus to catalog shoots and making homesick calls to her family in Puerto Rico. Things were not looking too good. One day, Smalls decided to motivate herself by filling a notebook page with a list of goals. They were big and highly specific. Model for Chanel. Get photographed by an iconic photographer like Mario Testino. Wear angel wings at the Victoria's Secret fashion show.

These aims might seem a tad unrealistic—but only to those who have not witnessed Smalls's unstoppable drive. Five years later, she has done all of those things, even adding in a few surreal bonus items (star in Beyoncé video, have Kanye West rap about you). But we're getting ahead of ourselves.

Few can electrify a catwalk like Smalls, now one of the world's top models. Her perfectly symmetrical face and golden skin have made her fashion's reigning It Girl—not to mention that body.

Lean but athletic, it's a work of art in its own right. (Women already ask trainers for the "Joan Smalls butt.") On the runway, Smalls moves with a confident, commanding gait that telegraphs pure power. The catwalk is about performance, and she brings to it the discipline and skill of an athlete.

Smalls, 26, the first Latina to front Estée Lauder's global campaign, is funny and friendly, with an easy laugh. But she is not coasting on her genetic good fortune. She treats her body like a fine machine that requires meticulous maintenance. In this philosophy, she's part of a new vanguard of clean-living models who are fully aware that their bodies are their business. Rather than living on cigarettes and hitting the clubs, they're waking up early to hit the gym.

The industry seemed to shift several years back, when the Council of Fashion Designers of America launched its health initiative to encourage a healthier lifestyle among models. Now you can see the results on Instagram, with @karliekloss, @karolinakurkova, @MirandaKerr and others sharing smoothie and salad pics.

As for Smalls, she doesn't drink (alcohol or caffeine) and is in bed most nights by 10:30. "I want to last in my career, and that relies on the way my body performs," she says. "So I need to take care of it." Her regimen includes regular workouts with trainer Marc Gordon. "I need to push myself," she says. She tries to eat plenty of fruit and vegetables, but confesses a weakness for Puerto Rican, Italian and Thai food, and a diabolical sweet tooth. "I don't want to be on such a strict diet that I don't have fun," she says. "So if I eat sweets, I'll just put in more of an effort when I go to the gym."

Smalls's height shot up when she was 13. At 14, after her sister was diagnosed with scoliosis, Smalls got checked out, too. When she saw the X-ray of her spine, she stared at it in shock: She had scoliosis in both her lower and upper spinal column. "The lower half of my spine was inside out," she says. "I started crying. I couldn't believe that was inside my body."

She quickly talked herself down. "I said, 'I'm not going to use this as a handicap. I'm going to push myself harder.'" She threw herself into rehabilitation exercises and stretches. To boost her strength, she took up boxing at 17. "People might think that because I'm skinny and tall, I'm fragile," she says. "But I always knew I wasn't. And it's comforting to know that I can throw a proper punch if I have to."